1. Field of the Invention
This invention relates to a method for preparing a catheter adapted to be inserted into the human body cavity, especially a guiding catheter for use in radiographic examination of the heart and surrounding tissues.
2. Prior Art
In the practice of percutaneous transluminal coronary angioplasty (PTCA), for example, a guiding catheter is first inserted until its distal end is located at the desired site, and a dilating catheter is then inserted into the lumen of the guiding catheter and guided to the site for dilating the stricture.
The guiding catheter for use in such operation typically has a tip portion of soft material such that it does not damage the vessel, heart or surrounding tissues upon insertion of the guiding catheter. Guiding catheters of this type are prepared in the prior art by constructing a catheter body from a resinous material such as flexible vinyl chloride and nylon, and impregnating an end portion of the catheter body with a plasticizer for plasticizing the end portion. This method has several drawbacks including inconsistent flexibility or softness imparted to the catheter end portion, difficulty to freely select the degree of softness, and complexity in the manufacturing process due to the addition of plasticizer impregnating step.
Another catheter manufacturing method is known in the art and described with reference to FIG. 6. There are prepared a catheter body 1 having a lumen 2 and an annular tip member 4 of a softer material than the catheter body 1. A core or skewer mandrel 6 is inserted through the catheter body 1 and the tip member 4. The mandrel 6 is moved into the cavity of a heated mold 8 to urge the tip member 4 and the catheter body 1 against the bottom of the mold cavity. The catheter body 1 is closely mated with the tip member 4 by further pulling the mandrel in a direction shown by arrow A. Then the tip member 4 and the adjacent portion of catheter body 1 are fuse welded at their mating ends and concurrently thermoformed on the outer surface.
This method often results in incomplete fusion welds partly because of the difference in material between the catheter body and the tip member. The tip member located close to the bottom of the mold cavity is first melted and bonded to the adjacent portion of catheter body 1 which has not been fully melted. In addition, the bonding area is small due to the fact that the tip member and the catheter body abut one another at their end surfaces. All these facts contribute to a reduced bond strength. The thermoformed tip members have varying length and poor outer appearance or surface smoothness, contributing to reduced productivity.